Bobbin brake



D. L. WENER BOBBIN BRAKE Oct. 5, 1954 Filed Feb. 9. 1953 FIG.

FIG-5 Patented Oct. 5, 1954 Ni'lED STATES PATENT OFFICE BOBBIN BRAKE David L. Wcner, Santa Ana, Calif.

Application February 9, 1953, Serial No. 335,829

1 Claim. 1

This invention relates to bobbin cases for sewing machines and has as its object the provision of simple and effective braking means for preventing over-running and back-lashing of thread running from a bobbin.

A further object is to provide for the purpose above stated a bobbin brake which has no moving parts, which requires no lubrication, which is entirely metallic and long-wearing, which does not touch the thread, and which cannot possibly entangle the thread.

In the accompanying drawing, illustrative of an embodiment of my invention in a now widely used type of bobbin case,

Fig. 1 is a plan view of a bobbin case, the bobbin itself not being shown;

Fig. 2 is a sectional View on the line 2-2 of Fig. 1;

Fig. 3 is a sectional view similar to Fig. 2 and on an enlarged scale, showing a bobbin mounted in the bobbin case and in a position indicating that the bobbin is rotating in response to threadtension; and

Fig. 4 is a sectional view similar to Fig. 3, illustrating the action of the brake upon the bobbin when thread tension is relaxed.

In general terms my invention comprises the installation of a simple magnet, which may be of bar-magnet type, in the end-wall of the bobbin case so that it will attract and draw the bobbin to it, applying friction to the adjacent end wall of the bobbin and tilting the bobbin upon the bobbin arbor to cause additional friction whenever relaxation of thread tension and concomitant reduction in rotational speed and gyroscopic force affecting the bobbin so permits.

The typical bobbin-case 5 selected for illustration of my invention has the usual thin cylindrical wall 5, and has a relatively thick end Wall E. A tubular arbor 8 extends centrally into the case 5 from the end wall 1. Those familiar with the art will understand that the arbor 8 rides rotatably upon a shuttle post (not shown) and is held thereupon by a sliding latch 9 operated by a lever 10 which is hinged to the end wall 7. The end-wall l is made relatively thick not only to support the arbor 8 but to accommodate and receive in embedded positions the latch 9 and hinged lever 40. A groove II in the end wall l communicates with a slot 12 in the cylindrical wall 6 to permit a tool or fingernail to be inserted behind a bobbin to remove the bobbin from the case. A thread aperture I3 is usually provided in the cylindrical wall 6 and a thread tension spring I 4 presses upon the thread emerg- 2 ing from the aperture l3. The spring I4 may be regulated by screws I5 set in a lug l6 raised from the walls 6 and l but the adjustable pressure merely governs tension on the thread outside of the case 5 and in no way regulates acceleration or deceleration of the bobbin.

The bobbin 2!], with thread 2| wound thereon, has spool ends 22 mounted on a hollow core 23 which rotates upon the arbor 8. It is customary that the core 23 is slightly oversize for the arbor 8, to avoid a tight bearing which would make difficult the insertion and removal of the bobbin 20 in and from the case 5. It is also not unusual to find the spool ends 22 slightly dished, generally inwardly toward the center of the bobbin at their outer edges, the dishing resulting either from pressure applied when the ends 22 are pressfitted on the core 23 in the process of manufacture or from subsequent handling. Bobbins as described are used over and over again, being rewound with thread when emptied, and to make them endurable the spool ends 22 are almost invariably made of steel, at least for commercial use, thus being responsive to magnetic attraction.

To the above described conventional construction, I add a magnet 25, mounted in the thick end wall 1 of the case 5, and preferably as remotely as practicable from the arbor 8. A preferred position for the magnet 25 is under the lug it which provides wall-thickness to prevent distortion of the case when the magnet is pressed into position. The magnet 25 may be a barmagnet; its polarity, although indicated, is not of importance. On the inner face 26 of the end wall 1, a groove 21 surrounds the pole (for example pole N) of the magnet. Preferably the pole N is substantially flush with the inner face 26, although it may protrude slightly so long as it does not interfere with the normal placement of the bobbin on the arbor 8. The groove 2'! provides an air-gap around the pole N, so that magnetic flux will pass through any magnetic body bridging the groove 21 and will not pass directly from the pole N to the face 26. The pole S may be flush with the outer face of the end wall i.

When the thread 2| is being unwound from the bobbin 20, the tension on the thread and the gyroscopic force acting on the rotating bobbin tend to ofiset the magnetic pull of the magnet 25 upon the adjacent spool end 22 and the bobbin tends to rotate in axial alignment with the arbor 8, as shown in Fig. 3. If the spool end 22 is dished inwardly there may be no contact between the spool end and the magnet 25; if there is contact, the friction will be light as the spool end will slide across the pole N. Tension upon the thread may easily be adjusted to compensate for any excessive friction by adjustment of the spring [4 by means of the screws 15, as is done with other types of constant pressure bobbin brakes but ordinarily not even this adjustment is necessary.

When tension upon the thread is slacked, the friction of the magnet 25 upon the spool end 22, or even the rotation of the spool end through the field of magnetic flux, causes rapid deceleration of the rotation of the bobbin. As the deceleration increases and the gyroscopic force upon the bobbin decreases, the magnet 25 pulls upon the spool end 22 and tilts the bobbin to the full extent that may be permitted by loose fit of the bobbin upon the arbor 8, as shown in Fig. 4. It will be understood that for purposes of illustration, the looseness of the bobbin 20 upon the arbor 8 is greatly exaggerated in both Fig. 3 and Fig. 4. The resulting misalignment rapidly increases the friction between the bobbin and the arbor and brings the bobbin to a stop. Actually, from whatever combination of frictional forces, the effect is nearly instantaneous, stopping rotation of the bobbin with less over-run than any other type of bobbin brake known to me.

If, as I believe, gyroscopic force is a factor in causing the bobbin to run more easily when the thread is being pulled off, and reduction in gyroscopic force enables the brake to act more effectively, that force is reasonably constant and available throughout the unwinding of a bobbin, as for a given rate of unwinding the rotational speed of the bobbin increases while the rotated mass decreases.

It will be obvious that my magnetic brake does not touch and therefor cannot foul the 4 thread. Unlike brakes of leather and other friction materials acting on the bobbin rather than on the thread, it requires no lubrication and receives and gives very little wear. When a bobbin 20 is in the case 5 and at rest, the bobbin itself acts as a keeper across the air-gap groove 21 and preserves the magnetic life of the brake. The preferred position of the magnet 25 closely adjacent the cylindrical wall 6 enables the magnet to exert not only the greatest retarding leverage by friction upon the spool end 22 but the greatest tilting leverage thereon.

I claim:

In a bobbin case for a bobbin having an end of magnetizable material, said case having an end wall normally parallel to and adjacent to said bobbin end, braking mechanism comprising in combination: means for supporting a bobbin for rotation relatively to said case in a slightly loose manner in which said bobbin may be canted relatively to the adjacent surface of said wall, and an opening formed in said wall disposed remotely radially from the axis of rotation of said bobbin and in a sector of said wall not exceeding a magnet mounted in said opening and having apole exposed through said inner surface of said case wall so as to make contact with the outer portion of an end of said bobbin, whereby said bobbin may be magnetically canted to increase frictional resistance between said bobbin and said case.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,316,444 Hayes Sept. 16, 1919 2,394,369 Colegrove Feb. 5, 1946 2,543,475 Slodysko Feb. 2'7, 1951 2,572,635 Lennox Oct. 23, 1951 

